Among women voters, 48 percent back Brown, while Mandel gets 31 percent of the female vote. Male voters are essentially tied, with 43 percent for Brown and 42 percent for Mandel.

Meanwhile, 46 percent of independent voters support Brown, while 28 percent support Mandel, according to the poll.

"Sen. Sherrod Brown retains his double-digit lead in the Ohio U.S. Senate race," said Peter A. Brown, assistant director of the Quinnipiac University Polling Institute.

He added, "At this point, Josh Mandel is not very well known and he can take some solace in the fact that Brown is not over the magic 50 percent threshold. There are seven months until Election Day, but Mandel needs to show some signs of life if he is going to make the Senate race competitive."

The survey of 1,246 Ohio voters was conducted from March 20th through 26th and has a margin of error of plus or minus 2.8 percentage points.

The results of the latest Quinnipiac survey compare to a January poll that showed Nelson with just a 41 percent to 40 percent lead over Mack.

Nelson leads 46 to 32 percent among women voters, while men split 41 to 41 percent. Nelson also has a 40 percent to 30 percent lead among independent voters, but 27 percent of independent voters are undecided.